A fundamental gap exists in our understanding of how polycystic ovarian syndrome (PCOS) develops. This knowledge is essential to preventing PCOS and co-morbidities such as type 2 diabetes and cardiovascular disease. PCOS patients exhibit a low-grade inflammatory state, which may be triggered by hyperinsulinemia, obesity, or other factors. The proposal's central hypothesis is that low-grade, chronic inflammation associated with PCOS causes ovarian dysfunction. This hypothesis has been formulated from preliminary data produced in the applicant's laboratory and will be tested by pursuing three specific aims: 1) Determine whether inflammation precedes ovarian dysfunction in a potential mouse model of PCOS. 2) Determine whether genetic inhibition of inflammation can prevent the development of PCOS symptoms. 3) Determine whether pharmacological inhibition of inflammation can prevent the development of PCOS symptoms. Under the first aim, a new mouse model of PCOS developed by the applicants will be used to examine the age-dependent onset of androgen excess and inflammation. Under the second aim, mouse strains lacking an inflammatory response will be used to test whether chronic immune system activation leads to PCOS. Finally, the third aim will test whether pharmacological inhibition of a key inflammatory pathway inhibits or treats PCOS. The proposed studies will be the first direct test of whether inflammation plays an essential role in PCOS development using an animal model. The results have the potential to shift current research and clinical practice paradigms by identifying a causative factor in PCOS development and testing a novel pharmacological treatment for the disorder. The findings from this research may help to identify women at risk for PCOS and prevent its development and co-morbidities, thus reducing healthcare costs and extending lives.